Tersa knives

[MikeJhn]

So what would I need to buy to convert my Kity 439 to the Tersa block system? I know I need a block and knives, but does anyone know what I need in the way of the block, is it on a shaft (dia) or do I need one with a what dia hole?

Mike

 

[memzey]

Who's got a wide Tersa block but never uses the full width?

My block is 12" but I generally only use about half of its width.

 

[OwenRS]

So what would I need to buy to convert my Kity 439 to the Tersa block system? I know I need a block and knives, but does anyone know what I need in the way of the block, is it on a shaft (dia) or do I need one with a what dia hole?

Mike

You would need a Brand New made to order Tersa Block on a New shaft. Simply add the bearings to the ends and install into your machine, Some machine castings need to have a hole drilled into one side to allow for the knives to be extracted but its not a major problem. With your machine it uses a 200mm wide knife I believe, so a small ish machine (good bit of kit the Kity machines).

You would have to weigh up the advantages over cost as a new block on a new shaft would be approx £350-400. Advantages are with the different grade of knives, the sound as the Tersa would be a fraction of the noise when running and also you would be able to change all knives in less than 5 minutes. No need to set or adjust your tables, simply slide the new knives in and start the machine up. Not a single bolt in sight.

 

[MikeJhn]

Jeremy

Thanks for the information, sounds a bit expensive for what is a budget machine, I don't have a particular problem setting my current knife set up, just use a piece of glass to get the knives level with the outfeed table, works well, will give it some more thought when I have my next project up and running.

Thanks again
Mike

 

[OwenRS]

Who's got a wide Tersa block but never uses the full width?

My block is 12" but I generally only use about half of its width.

Tersa Money Saving Tip No.2

We all know of the 4 major grades of Genuine Tersa knives, Chrome, HSS, M+ and the Carbide. People are hesitant at times to step up the grades and to see the advantages each grade gives. Remember one knife will do all but not to its optimum. To Save the most amount of Money you will have to match the right grade of Knife to the right application.

Right that all said and done. Lets say on your 12" (310mm) wide planer you have always run the HSS grade and machined a variety of timbers. The next job you pick up is for a batch of planed up Oak of lets say 2" x 1" and you want the best finish, and for the knives to last a long time due to you having a good pack of it to put through. The best blade for this would be the Carbide which do carry a premium to buy. The second best would be the M+ grade which will give the same style of finish but this will have a large come down from the Carbides tool life and need changing more regular.

Money Saving Tip coming right up. . . . . Who says you have to buy a 12" (310mm) carbide knife???? Just by an 80mm carbide knife and slide it to one end of the block and then buy a standard 230mm Budget Chrome knife and insert it into the same knife slot in the block. You can then choose to do this in all 4 of your knife slots or choose to follow Tersa Money Saving Tip No.1 and repeat this in two of your four slots with the other two simply having 12" (310mm) chrome knives in. Double saving.

From a machinist point of view I would then make an MDF board that hooks over my infeed table limiting the table width to the 80mm on the same side as the location of the carbide knives. I know some ones bound to point out I said we have 2"(50mm) wide Oak and I have suggested an 80mm knife, this is just in case timbers wonder while passing through the machine. If you make the MDF infeed limiter right you could reduce the 80mm Carbide knife further saving you even more pennies.

This method can be applied to all Genuine Tersa grades due to the high precision of all of them from one manufacturer and it is not just limited to the Carbide grades. Simply follow the above for the M+ or the HSS.

Again Please Keep Viewing For More Money Saving Tersa Tips.

 

[memzey]

Wow. I'd never even considered mixing the types of blade in the same slot. I guess this only works as the slots and blades are machined to such close tolerances?

 

[deema]

Jeremy, as a long time user of Tersa knives, I take my hat off to you, I've learnt more from your posts than in all my previous years put together using them. Thank you.

 

[memzey]

I'm a recent adopter of the Tersa system but concur with deema above. Jeremy has definitely opened my eyes to possibilities I wasn't aware of before. Perhaps this thread could be made a sticky to help others not aware of these options? Everyone could then add their own tips going forward?

 

[ColeyS1]

Regarding tip number one, if only one blade is doing the cutting, and the others are merely blunt/knackered just filling the hole, wouldn't the one blade doing the cutting wear out much quicker ? So instead of 4 blades of the same, for example lasting 40 hrs, would one blade with 3 inferior blunt blades last only 10 hours ? Does that make sense?

Tip number two sounds feasible. The only thing I'd add is just be careful if you do start using short lengths of blade. I've been destracted and had to wiggle a board back in line when thicknessing and that managed to move a long tersa knife enough to start rubbing the guard. Shorter lengths I imagine you'd need to be even more cautious.

Coley

 

[custard]

Regarding tip number one, if only one blade is doing the cutting, and the others are merely blunt/knackered just filling the hole, wouldn't the one blade doing the cutting wear out much quicker ? So instead of 4 blades of the same, for example lasting 40 hrs, would one blade with 3 inferior blunt blades last only 10 hours ? Does that make sense?

I've been listening to the debate about which planer knives actually do the cutting for forty years, and unless spiral cutters take over the world I expect it'll still be going strong in another forty!

For what it's worth I've come to the conclusion that feed speed has a bearing on the issue. So the theory that a single knife does the lion's share of the work is more true for a cabinet maker running his thicknesser at a slow speed, than it is for a joiner running his thicknesser at a fast speed.

 

[ColeyS1]

I'm not sure I see the advantage of using less cutters unless the feed speed is reduced. Having one of the blades stick out slightly more than the rest also leaves my mind spinning. The whole point in making machines with more knives cutting exactly the same (or so I thought) was to produce a cleaner finish. Stick in blunt blades,without lowering the feed speed HAS to have an effect on the quality of finish.

Coley

 

[OwenRS]

I'm unsure where blunt or knackard knives are mentioned???? Tip one mentions tips wearing behind others but we are talking such small amounts it won't be rounding the edges off to a blunt knife. Remember Everything has a tolerance, us humans fit them.

Lets through another twist onto the idea.

A goof few years back I used to run a massive timber mill and had my hands dirty on the good old fashioned serrated knife profile grinder. We had 4 knife blocks and via the serrations would fit 4 knives into a cutter head all on the same serration to give the same projection of the blanks and to help statically balance the blocks. Plastic template made by the table top CNC and away we go grinding my profile.

We used roughing wheels and then finishing wheels and I can confirm from my own eyes and hands it is IMPOSSIBLE to get each knife to exactly the same length of projection. For one simple reason , for every cut the grinding wheel made in my knife the grinding wheel also wore down in diameter and grit was left in the water to clean up later. So by the time the grinding wheel reached knife 2, 3 and then 4 the wheel was a smaller diameter and each knife slightly longer. Making sense so far I hope.

We had a projector setting stand and could see this small amount at 40 times its true size. While this block could easily be taken and put on our small batch machine running 10-12 meters a minute it could not run on the larger machine that did up to 60 meters a minute. On the small machine 3 of the knives (knife 1,2 and 3) are now shorter from the grinding process than knife 4. These first 3 are purely there to rough out the work as they rotated but the finish on your timber is created by knife 4 the longest knife. When knife 4 wears back over time knife 3 kicks in and so on until knife 1 is blunt and the hole set up needs grinding again.

This is exactly what is happening in the Tersa. A super human tolerance manufactured knife that us Humans with fingers, thumbs, dust, and sap resin fit into a slot and say by the power of my start button hold these knives in the same place, Please.
I end my essay with one of my starting quotes. Everything has a Tolerance and Tersa is no exception.

 

[ScottandSargeant]

There are some shear cut spirals around which do give a really good finish... But not as good as Tersa... They are capable of much heavier cuts than Tersa is capable of handling... There are also some terrible ones..
Horses for courses etc etc